Electrolyte membrane for lithium-air battery, method of manufacturing same and lithium-air battery comprising same

ABSTRACT

Disclosed are an electrolyte membrane for a lithium-air battery, a method of manufacturing the same, a cathode for a lithium-air battery, a method of manufacturing the same, and a lithium-air battery including the electrolyte membrane and the cathode. Particularly, the lithium-air battery includes i) an electrolyte membrane, which is manufactured using an inorganic melt admixture including two or more nitrogen-oxide compounds and thus may have a very low eutectic point, and ii) a cathode, which is manufactured by reducing a metal at a fast speed on a carbon material. As such, the lithium-air battery is capable of stably operating even at low temperatures and providing high power output.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority based on Korean PatentApplication No. 10-2020-0066555, filed on Jun. 2, 2020, the entirecontent of which is incorporated herein for all purposes by thisreference.

TECHNICAL FIELD

The present invention relates to an electrolyte membrane for alithium-air battery, a method of manufacturing the same, a cathode for alithium-air battery, a method of manufacturing the same, and alithium-air battery including the electrolyte membrane and the cathode.Particularly, the lithium-air battery may include i) an electrolytemembrane, which may be manufactured using an inorganic melt admixture(e.g., solution) including two or more nitrogen-oxide compounds and thusmay have a very low eutectic point, and ii) a cathode, manufactured byreducing a metal at a fast speed on a carbon material. As such, thelithium-air battery is capable of stably operating even at lowtemperatures and providing high power output.

BACKGROUND

Lithium-air secondary batteries have greater energy density thanlithium-ion secondary batteries and have the advantage of being able tooperate using oxygen in the air. However, side reactions between thecarbon-based electrode and the organic-solvent-based electrolyte mayoccur to deteriorate the performance of the batteries, and research intosolving this problem has been ongoing.

An organic-solvent-based liquid electrolyte typically used inlithium-air secondary batteries is highly volatile, so it easilyevaporates in the course of charging and discharging, undergoes loss dueto leakage, and is unstable at high temperatures, making it difficult tooperate.

SUMMARY

In one preferred aspect, provided is a lithium-air battery capable ofoperating under various temperature conditions ranging from lowtemperatures to high temperatures.

In one preferred aspect, provided is a method of manufacturing a cathodethrough a Joule heating reaction capable of synthesizing a catalyst in ashort time.

The objectives of the present invention are not limited to theforegoing, and will be able to be clearly understood through thefollowing description and to be realized by the means described in theclaims and combinations thereof.

In an aspect, provided is a method of manufacturing an electrolytemembrane for a lithium-air battery. The method may include preparing aninorganic salt, preparing an inorganic melt admixture (e.g., solution)including the inorganic salt (e.g., by melting the inorganic salt),immersing a separator in the inorganic melt admixture, and drying theimmersed separator.

The inorganic salt may include at least two nitrogen-oxide compounds.

The term “nitrogen-oxide compounds” as used herein refers to a compoundor a salt that is formed with i) a cationic metal (e.g., alkali metal oralkali earth metal cation) and ii) an anionic nitrate (NO₃ ⁻) or anionicnitrite (NO₂ ⁻). Exemplary nitrogen-oxide compounds include the saltformed of the metal cation (e.g., Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺,Sr²⁺, or Ba²⁺) and the anionic nitrate (NO₃ ⁻) or the anionic nitrite(NO₂ ⁻).

The inorganic salt may include one or more selected from the groupconsisting of lithium nitrate (LiNO₃), potassium nitrate (KNO₃),potassium nitrite (KNO₂), cesium nitrate (CsNO₃), sodium nitrate(NaNO₃), and calcium nitrate (Ca(NO₃)₂).

The inorganic salt may include two types of nitrogen-oxide compounds,three types of nitrogen-oxide compounds, four types of nitrogen-oxidecompounds, and five types of nitrogen-oxide compounds.

The two types of the nitrogen-oxide compounds may suitably includelithium nitrate and potassium nitrate, the three types of thenitrogen-oxide compounds may suitably include lithium nitrate, potassiumnitrate and sodium nitrate, may include lithium nitrate, potassiumnitrate and calcium nitrate, or may suitably include lithium nitrate,potassium nitrite and cesium nitrate, the four types of thenitrogen-oxide compounds may suitably include lithium nitrate, potassiumnitrate, sodium nitrate and calcium nitrate, and the five types of thenitrogen-oxide compounds may suitably include lithium nitrate, potassiumnitrate, cesium nitrate, sodium nitrate and calcium nitrate.

The inorganic salt may suitably include three types of thenitrogen-oxide compounds including lithium nitrate, potassium nitriteand cesium nitrate, four types of the nitrogen-oxide compounds includinglithium nitrate, potassium nitrate, sodium nitrate and calcium nitrate,or five types of the nitrogen-oxide compounds including lithium nitrate,potassium nitrate, cesium nitrate, sodium nitrate and calcium nitrate.

The three types of the nitrogen-oxide compounds may include an amount ofabout 29 mol % to 35 mol % of lithium nitrate, an amount of about 51 mol% to 56 mol % of potassium nitrite and an amount of about 10 mol % to 15mol % of cesium nitrate, the four types of the nitrogen-oxide compoundsmay include an amount of about 27 mol % to 31 mol % of lithium nitrate,an amount of about 38 mol % to 50 mol % of potassium nitrate, an amountof about 11 mol % to 20 mol % of sodium nitrate and an amount of about10 mol % to 13 mol % of calcium nitrate, and the five types of thenitrogen-oxide compounds may include an amount of about 14 mol % to 17mol % of lithium nitrate, an amount of about 29 mol % to 31 mol % ofpotassium nitrate, an amount of about 28 mol % to 32 mol % of cesiumnitrate, an amount of about 9 mol % to 11 mol % of sodium nitrate and anamount of about 13 mol % to 18 mol % of calcium nitrate. All the mol %based on the total mole of the nitrogen-oxide compounds.

The inorganic salt may have a eutectic point of about 130° C. or less.

The inorganic salt may have a eutectic point of about 100° C. or less.

In an aspect, provided is an electrolyte membrane for a lithium-airbattery manufactured by the method described herein.

In an aspect, provided is a method of manufacturing a cathode for alithium-air battery. The method may include preparing a metal precursoradmixture (e.g., solution) including a metal precursor, manufacturing anelectrode slurry including the metal precursor admixture and a carbonmaterial, applying the electrode slurry on a substrate, and reducing ametal ion by applying current to the applied electrode slurry.

The metal precursor may include one or more selected from the groupconsisting of platinum (Pt), rubidium (Ru), palladium (Pd), rhodium(Rh), nickel (Ni), cobalt (Co), iron (Fe), copper (Cu), and silver (Ag).

The carbon material may include one or more selected from the groupconsisting of natural graphite, artificial graphite, carbon nanotubes,reduced graphene oxide (rGO), carbon fiber, carbon black, Ketjen black,acetylene black, mesoporous carbon, graphite, Denka black, fullerene,and activated carbon.

The electrode slurry may suitably include the metal precursor in anamount of about 40 parts by weight to 60 parts by weight based on 100parts by weight of the carbon material.

The current may be applied for about 0.1 sec to 60 sec.

The magnitude of the current may be about 6 A to 10 A.

In an aspect, provided is a cathode for a lithium-air batterymanufactured by the method described above.

In an aspect, provided is a lithium-air battery that may include acathode including a carbon material, an anode disposed to face thecathode and including a lithium metal that receives and releases alithium ion, and the electrolyte membrane described herein interposedbetween the cathode and the anode.

The carbon material may include one or more selected from the groupconsisting of natural graphite, artificial graphite, carbon nanotubes,reduced graphene oxide (rGO), carbon fiber, carbon black, Ketjen black,acetylene black, mesoporous carbon, graphite, Denka black, fullerene,and activated carbon.

According to various exemplary embodiments of the present invention, alithium-air battery capable of operating under various temperatureconditions ranging from low temperatures to high temperatures may beprovided.

According to various exemplary embodiments of the present invention, amethod of manufacturing a cathode through a Joule heating reactioncapable of synthesizing a catalyst in a short time may be provided.

The effects of the present invention are not limited to the foregoing,and should be understood to include all effects that can be reasonablyanticipated from the following description.

Other aspects of the invention are disclosed infra.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an exemplary process of manufacturing an exemplaryelectrolyte membrane according to an exemplary embodiment of the presentinvention;

FIG. 2 shows an exemplary configuration of an exemplary electrolytemembrane according to an exemplary embodiment of the present invention;

FIG. 3 shows an exemplary process of manufacturing an exemplary cathodeaccording to an exemplary embodiment of the present invention;

FIG. 4 shows an exemplary configuration of an exemplary cathodeaccording to an exemplary embodiment of the present invention;

FIGS. 5A and 5B are graphs showing the results of Test Example 1;

FIGS. 6A and 6B are graphs showing the results of Test Example 2;

FIGS. 7A to 7F are graphs showing the results of Test Example 3;

FIGS. 8A and 8B are graphs showing the results of Test Example 4;

FIGS. 9A and 9B are graphs showing the results of Test Example 5; and

FIGS. 10A to 10C are SEM images showing the cathode of the presentinvention in Test Example 6.

DETAILED DESCRIPTION

The above and other objectives, features and advantages of the presentinvention will be more clearly understood from the following preferredembodiments taken in conjunction with the accompanying drawings.However, the present invention is not limited to the embodimentsdisclosed herein, and may be modified into different forms. Theseembodiments are provided to thoroughly explain the invention and tosufficiently transfer the spirit of the present invention to thoseskilled in the art.

Throughout the drawings, the same reference numerals will refer to thesame or like elements. For the sake of clarity of the present invention,the dimensions of structures are depicted as being larger than theactual sizes thereof. It will be understood that, although terms such as“first”, “second”, etc. may be used herein to describe various elements,these elements are not to be limited by these terms. These terms areonly used to distinguish one element from another element. For instance,a “first” element discussed below could be termed a “second” elementwithout departing from the scope of the present invention. Similarly,the “second” element could also be termed a “first” element. As usedherein, the singular forms are intended to include the plural forms aswell, unless the context clearly indicates otherwise.

It will be further understood that the terms “comprise”, “include”,“have”, etc., when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, components, orcombinations thereof, but do not preclude the presence or addition ofone or more other features, integers, steps, operations, elements,components, or combinations thereof. Also, it will be understood thatwhen an element such as a layer, film, area, or sheet is referred to asbeing “on” another element, it can be directly on the other element, orintervening elements may be present there between. Similarly, when anelement such as a layer, film, area, or sheet is referred to as being“under” another element, it can be directly under the other element, orintervening elements may be present there between.

Unless otherwise specified, all numbers, values, and/or representationsthat express the amounts of components, reaction conditions, polymercompositions, and mixtures used herein are to be taken as approximationsincluding various uncertainties affecting measurement that inherentlyoccur in obtaining these values, among others, and thus should beunderstood to be modified by the term “about” in all cases. Furthermore,when a numerical range is disclosed in this specification, the range iscontinuous, and includes all values from the minimum value of said rangeto the maximum value thereof, unless otherwise indicated. Moreover, whensuch a range pertains to integer values, all integers including theminimum value to the maximum value are included, unless otherwiseindicated.

Further, unless specifically stated or obvious from context, as usedherein, the term “about” is understood as within a range of normaltolerance in the art, for example within 2 standard deviations of themean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%,3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unlessotherwise clear from the context, all numerical values provided hereinare modified by the term “about.”

In the present specification, when a range is described for a variable,it will be understood that the variable includes all values includingthe end points described within the stated range. For example, the rangeof “5 to 10” will be understood to include any subranges, such as 6 to10, 7 to 10, 6 to 9, 7 to 9, and the like, as well as individual valuesof 5, 6, 7, 8, 9 and 10, and will also be understood to include anyvalue between valid integers within the stated range, such as 5.5, 6.5,7.5, 5.5 to 8.5, 6.5 to 9, and the like. Also, for example, the range of“10% to 30%” will be understood to include subranges, such as 10% to15%, 12% to 18%, 20% to 30%, etc., as well as all integers includingvalues of 10%, 11%, 12%, 13% and the like up to 30%, and will also beunderstood to include any value between valid integers within the statedrange, such as 10.5%, 15.5%, 25.5%, and the like.

Provided herein are a method of manufacturing an electrolyte membranefor a lithium-air battery, an electrolyte membrane manufactured thereby,a method of manufacturing a cathode for a lithium-air battery, a cathodemanufactured thereby, and a lithium-air battery including theelectrolyte membrane and the cathode.

FIGS. 1 and 3 are flowcharts showing exemplary processes ofmanufacturing the electrolyte membrane and the cathode according toexemplary embodiments of the present invention, respectively. Withreference to these drawings, individual steps are specified below.

Method of Manufacturing Lithium-Air Battery

The method of manufacturing a lithium-air battery may include i) amethod of manufacturing an electrolyte membrane and ii) a method ofmanufacturing a cathode.

The method of manufacturing the electrolyte membrane may includepreparing an inorganic salt, preparing an inorganic melt admixture(e.g., solution) including the inorganic salt, by melting the inorganicsalt, immersing a separator in the inorganic melt admixture, and dryingthe immersed separator. The method of manufacturing the cathode mayinclude preparing a metal precursor admixture (e.g., solution) includinga metal precursor, preparing an electrode slurry including mixing themetal precursor admixture and a carbon material, applying the electrodeslurry on a substrate, and reducing a metal ion by applying current tothe applied electrode slurry.

The method of manufacturing the electrolyte membrane and the method ofmanufacturing the cathode are separately described below.

Method of Manufacturing Electrolyte Membrane for Lithium-Air Battery

The method of manufacturing the electrolyte membrane for a lithium-airbattery may include preparing an inorganic salt, preparing an inorganicmelt admixture (e.g., solution) including the inorganic salt, forexample, by melting the inorganic salt, immersing a separator in theinorganic melt admixture, and drying the immersed separator.

FIG. 1 shows an exemplary process of manufacturing an exemplaryelectrolyte membrane for a lithium-air battery according to an exemplaryembodiment of the present invention. With reference thereto, individualsteps are described, and the electrolyte membrane manufactured therebyis described with reference to FIG. 2.

Preparation of Inorganic Salt

An inorganic salt may be prepared, and the inorganic salt may preferablyinclude a nitrogen-oxide compound.

The nitrogen-oxide compound may include one or more selected from thegroup consisting of lithium nitrate (LiNO₃), potassium nitrate (KNO₃),potassium nitrite (KNO₂), cesium nitrate (CsNO₃), sodium nitrate(NaNO₃), and calcium nitrate (Ca(NO₃)₂), and preferably includes two ormore different nitrogen-oxide compounds.

The inorganic salt may include two types of the nitrogen-oxidecompounds, three types of the nitrogen-oxide compounds, four types ofthe nitrogen-oxide compounds, and five types of the nitrogen-oxidecompounds. Preferably, the inorganic salt may include three to fivetypes of the nitrogen-oxide compounds.

The two types of the nitrogen-oxide compounds may suitably includelithium nitrate and potassium nitrate, the three types of thenitrogen-oxide compounds may suitably include lithium nitrate, potassiumnitrate and sodium nitrate, include lithium nitrate, potassium nitrateand calcium nitrate, or include lithium nitrate, potassium nitrite andcesium nitrate, the four types of the nitrogen-oxide compounds maysuitably include lithium nitrate, potassium nitrate, sodium nitrate andcalcium nitrate, and the five types of the nitrogen-oxide compounds maysuitably include lithium nitrate, potassium nitrate, cesium nitrate,sodium nitrate and calcium nitrate.

The two types of the nitrogen-oxide compounds may suitably include anamount of about 40 mol % to 43 mol % of lithium nitrate and an amount ofabout 57 mol % to 60 mol % of potassium nitrate. In the case in whichthe composition ratio thereof falls out of the above range, the area ofthe eutectic point in the phase equilibrium may be changed, which causesa problem in which the melting point is greatly changed, making itimpossible to attain the desired effects of the present invention.

The three types of the nitrogen-oxide compounds may suitably include anamount of about 29 mol % to 31 mol % of lithium nitrate, an amount ofabout 51 mol % to 53 mol % of potassium nitrate and an amount of about17 mol % to 19 mol % of sodium nitrate; suitably include an amount ofabout 30 mol % to 32 mol % of lithium nitrate, an amount of about 57 mol% to 59 mol % of potassium nitrate and an amount of about 10 mol % to 12mol % of calcium nitrate; or suitably include an amount of about 29 mol% to 35 mol % of lithium nitrate, an amount of about 51 mol % to 56 mol% of potassium nitrite and an amount of about 10 mol % to 15 mol % ofcesium nitrate.

The four types of the nitrogen-oxide compounds may suitably include anamount of about 27 mol % to 31 mol % of lithium nitrate, an amount ofabout 38 mol % to 50 mol % of potassium nitrate, an amount of about 11mol % to 20 mol % of sodium nitrate and an amount of about 10 mol % to13 mol % of calcium nitrate.

The five types of the nitrogen-oxide compounds may suitably include anamount of about 14 mol % to 17 mol % of lithium nitrate, an amount ofabout 29 mol % to 31 mol % of potassium nitrate, an amount of about 28mol % to 32 mol % of cesium nitrate, an amount of about 9 mol % to 11mol % of sodium nitrate and an amount of about 13 mol % to 18 mol % ofcalcium nitrate.

The eutectic point may vary depending on the type, number and amount ofthe nitrogen-oxide compounds included in the inorganic salt.

The eutectic point of the inorganic salt including two or more of thenitrogen-oxide compounds may be about 130° C. or less.

The eutectic point of the two types of the nitrogen-oxide compounds maypreferably be about 125° C. or less, the eutectic point of the threetypes of the nitrogen-oxide compounds may preferably be about 90 to 120°C., the eutectic point of the four types of the nitrogen-oxide compoundsmay preferably be about 95° C. or less, and the eutectic point of thefive types of the nitrogen-oxide compounds may preferably be about 80°C. or less.

The eutectic point of the inorganic salt may preferably be about 100° C.or less. The inorganic salt may include three types of thenitrogen-oxide compounds composed of lithium nitrate, potassium nitriteand cesium nitrate and having a eutectic point of about 90 to 95° C.,four types of the nitrogen-oxide compounds composed of lithium nitrate,potassium nitrate, sodium nitrate and calcium nitrate and having aeutectic point of about 95° C. or less, or five types of thenitrogen-oxide compounds composed of lithium nitrate, potassium nitrate,cesium nitrate, sodium nitrate and calcium nitrate and having a eutecticpoint of about 80° C. or less.

Manufacture of Inorganic Melt Admixture

The inorganic salt may be melted to afford an inorganic melt admixture.For example, the inorganic salt including two or more nitrogen-oxidecompounds may be melted to afford an inorganic melt admixture. Thecomposition of the nitrogen-oxide compounds included in the inorganicmelt admixture is the same as the composition of the nitrates includedin the inorganic salt.

Immersion

A separator may be immersed in the inorganic melt admixture preparedabove, so the separator may be wetted with the inorganic melt admixtureand thus the inorganic melt admixture may be incorporated into andattached to the inner and outer portions of the separator.

Any separator may be used without limitation, so long as it is typicallyuseful in fuel cell fields and is resistant to temperatures of about110° C. or greater, and about preferably 130° C. or greater. Since theseparator is impregnated with the inorganic melt admixture obtainedthrough melting at a high temperature, it has to possess sufficient heatresistance to withstand the heat of the inorganic melt admixture. Theseparator may preferably include glass fiber.

Drying

The separator may be taken out of the inorganic melt admixture and driedto afford an electrolyte membrane.

The drying may be preferably performed at a temperature of about 60° C.or less in a vacuum, and the drying process in the present invention isnot particularly limited.

Electrolyte Membrane for Lithium-Air Battery

The electrolyte membrane for a lithium-air battery may be manufacturedthrough the method described herein, and the electrolyte membrane mayinclude a separator and an inorganic melt admixture. The inorganic meltadmixture may suitably include two to five types of the nitrogen-oxidecompounds, and preferably include three to five types of thenitrogen-oxide compounds.

FIG. 2 shows an exemplary electrolyte membrane for a lithium-air batteryaccording to an exemplary embodiments of the present invention. Forexample, the inorganic melt admixture may be incorporated into andattached to the inner and outer portions of the separator having porestherein.

Method of Manufacturing Cathode for Lithium-Air Battery

The method of manufacturing the cathode for a lithium-air battery mayinclude preparing a metal precursor admixture (e.g., solution) includinga metal ion, preparing an electrode slurry including the metal precursoradmixture and a carbon material, applying the electrode slurry on asubstrate, and reducing the metal ion by applying current to the appliedelectrode slurry.

FIG. 3 is a flowchart of an exemplary process of manufacturing anexemplary cathode according to an exemplary embodiment of the presentinvention. With reference thereto, individual steps are described, andthe cathode manufactured thereby is described with reference to FIG. 4.

Preparation of Metal Precursor Admixture

A metal precursor admixture including a metal ion may be prepared. Themetal precursor admixture may include a metal precursor.

The metal precursor may suitably include one or more metal selected fromthe group consisting of platinum (Pt), rubidium (Ru), palladium (Pd),rhodium (Rh), nickel (Ni), cobalt (Co), iron (Fe), copper (Cu), andsilver (Ag).

The metal precursor is not particularly limited, so long as it iscapable of being coupled with the above metal and of being dissolved inwater (H₂O). For example, the metal precursor includes a form in whichnitrate (NO₃ ⁻), nitrite (NO₂ ⁻), chloride (Cl⁻), or the like is coupledwith the metal. For example, the metal may be present in an ionic stateby being coupled with the anion, such as nitrate, nitrite or chloride.

Manufacture of Electrode Slurry

The metal precursor admixture may be mixed with a carbon material toafford an electrode slurry.

The carbon material may suitably include one or more selected from thegroup consisting of natural graphite, artificial graphite, carbonnanotubes, reduced graphene oxide (rGO), carbon fiber, carbon black,Ketjen black, acetylene black, mesoporous carbon, graphite, Denka black,fullerene, and activated carbon.

The metal precursor of the present invention may preferably be mixed inan amount of 40 parts by weight to 60 parts by weight based on 100 partsby weight of the carbon material.

Application of Electrode Slurry

The electrode slurry may be applied on a substrate.

The type of substrate is not particularly limited in the presentinvention, and any substrate may be used, so long as it provides a baseon which it is possible to uniformly apply the electrode slurry and isconductive.

The process of applying the electrode slurry is not particularlylimited, and any process may be performed in the present invention, solong as it is typically able to apply an electrode slurry.

Reduction

The current may be applied to the applied electrode slurry and thus themetal ion may be reduced. Particularly, a metal catalyst may besynthesized on the surface of the carbon material through a Jouleheating reaction.

The current may be applied to both ends of the electrode slurry, whichmay be applied and uniformly spread on the substrate. The magnitude ofthe current that is applied may preferably be about 6 A to 10 A forabout 0.1 sec to 60 sec.

Cathode for Lithium-Air Battery

A cathode for a lithium-air battery according to the present inventionmay be manufactured through the method described herein, and the cathodemay include a carbon material and a metal attached to the surface of thecarbon material. The metal may suitably include one or more selectedfrom the group consisting of platinum (Pt), rubidium (Ru), palladium(Pd), rhodium (Rh), nickel (Ni), cobalt (Co), iron (Fe), copper (Cu),and silver (Ag).

FIG. 4 shows an exemplary cathode for a lithium-air battery according toan exemplary embodiment of the present invention. With referencethereto, the metal ion is reduced and precipitated as metal particles onthe surface of the carbon material forming the cathode skeleton.

Lithium-Air Battery

A lithium-air battery includes a cathode including a carbon material, ananode disposed to face the cathode and including a lithium metal thatreceives and releases a lithium ion, and an electrolyte membraneinterposed between the cathode and the anode.

The carbon material included in the cathode may suitably include one ormore selected from the group consisting of natural graphite, artificialgraphite, carbon nanotubes, reduced graphene oxide (rGO), carbon fiber,carbon black, Ketjen black, acetylene black, mesoporous carbon,graphite, Denka black, fullerene, and activated carbon.

The cathode of the present invention may include a carbon materialhaving metal particles on the surface thereof.

The metal particles may be obtained as being precipitated by reducingthe metal ion on the surface of the carbon material by the currentapplied from the outside, and may include one or more selected from thegroup consisting of platinum (Pt), rubidium (Ru), palladium (Pd),rhodium (Rh), nickel (Ni), cobalt (Co), iron (Fe), copper (Cu), andsilver (Ag).

The anode is not limited, so long as it is of a type that is typicallyuseful for a lithium-air battery.

The electrolyte membrane may include a separator and an inorganic meltadmixture. The inorganic melt admixture may include two to five types ofthe nitrogen-oxide compounds, and preferably three to five types of thenitrogen-oxide compounds described herein.

EXAMPLE

A better understanding of the present invention will be given throughthe following examples. However, these examples are merely set forth toillustrate the present invention, and are not to be construed aslimiting the scope of the present invention.

Preparation Example 1 and Preparation Example 2

An inorganic salt including a combination of nitrates as shown in Table1 below was prepared, and was then melted to afford an inorganic meltadmixture. Thereafter, a glass fiber film was immersed in the inorganicmelt admixture and was then slowly dried at room temperature, thusmanufacturing an electrolyte membrane.

TABLE 1 nitrogen-oxide LiNO₃ KNO₃ CsNO₃ NaNO₃ Ca(NO₃)₂ compounds (mol %)(mol %) (mol %) (mol %) (mol %) Preparation 43 57 — — — Example 1Preparation 15 30 29 10 16 Example 2

Preparation Example 3

A carbon paper (P50) including a carbon material (Super P) was prepared,and a metal precursor solution, RuCl₃*H₂O, was mixed in an amount of 50parts by weight based on 100 parts by weight of the carbon material toafford an electrode slurry. The electrode slurry was applied on thecarbon paper using a doctor blade. Thereafter, both ends of the carbonpaper and the electrode slurry applied on the carbon paper wereconnected with a copper foil through which external current was made toflow, after which current of 7 A was applied thereto and the temperatureof the electrode slurry was elevated, thereby manufacturing a cathode.

Preparation Example 4

An anode including lithium metal foil and a cathode were joined torespective sides of the electrolyte membrane manufactured in PreparationExample 1, thus manufacturing a lithium-air battery. Here, the cathodewas a carbon paper coated with RuO₂ and PVDF (polyvinylidene fluoride).

Preparation Example 5

An anode including lithium metal foil and a cathode were joined torespective sides of the electrolyte membrane manufactured in PreparationExample 2, thus manufacturing a lithium-air battery. Here, the cathodewas a carbon paper coated with RuO₂ and PVDF (polyvinylidene fluoride).

Preparation Example 6

An anode including lithium metal foil and the cathode manufactured inPreparation Example 3 were joined to respective sides of the electrolytemembrane manufactured in Preparation Example 1, thus manufacturing alithium-air battery.

Preparation Example 7

An anode including lithium metal foil and the cathode manufactured inPreparation Example 3 were joined to respective sides of the electrolytemembrane manufactured in Preparation Example 2, thus manufacturing alithium-air battery.

Test Example 1

The melting point of the electrolyte membrane manufactured in each ofPreparation Example 1 and Preparation Example 2 was measured usingdifferential scanning calorimetry (DSC). As shown in FIGS. 5A and 5B,showing the results thereof, the eutectic point was 130° C. inPreparation Example 1 (FIG. 5A) using the inorganic salt including twotypes of salts, and was 68° C. in Preparation Example 2 (FIG. 5B) usingthe inorganic salt including five types of salts.

Test Example 2

The lithium-air batteries manufactured in Preparation Example 4 andPreparation Example 5 were charged and discharged at 100° C., 120° C.and 150° C. The results thereof are shown in FIGS. 6A and 6B.Particularly, FIG. 6A is a graph showing the voltage depending oncapacity measured during charge and discharge of the lithium-air batteryincluding the electrolyte membrane manufactured using the inorganic saltincluding two types of salts, and FIG. 6B is a graph showing the voltagedepending on capacity measured during charge and discharge of thelithium-air battery including the electrolyte membrane manufacturedusing the inorganic salt including five types of salts.

As shown in the graph of FIG. 6B, the charge/discharge voltagedifference greatly decreased with an increase in the operatingtemperature.

Test Example 3

The charge/discharge test was performed on the lithium-air battery ofPreparation Example 5, and the gas evolution was measured at the sametime. The results thereof are shown in FIGS. 7A to 7F. Particularly,FIG. 7A shows a change in voltage when charging and discharging thelithium-air battery of Preparation Example 4 at an operating temperatureof 150° C., FIG. 7C shows a change in voltage when charging anddischarging the lithium-air battery of Preparation Example 5 at anoperating temperature of 150° C., and FIG. 7E shows a change in voltagewhen charging and discharging the lithium-air battery of PreparationExample 5 at an operating temperature of 100° C. Particularly, FIGS. 7A,7C and 7E show the change in voltage depending on capacity when chargingand discharging the lithium-air battery at respective operatingtemperatures. The results of gas evolution during respective tests atthe same time are shown in order in FIGS. 7B, 7D and 7F.

Based on the results of FIGS. 7A to 7F, in both of the inorganic saltincluding two types of salts (nitrogen-oxide compounds) and theinorganic salt including five types of salts (nitrogen-oxide compounds)at the operating temperature of 150° C., oxygen reached the theoreticalvalue, but when the operating temperature was low, specifically 100° C.,the oxygen evolution was slightly decreased.

Test Example 4

The lithium-air battery of Preparation Example 7 was charged anddischarged and analyzed for gas evolution in the same manner as in TestExample 3. The results thereof are shown in FIGS. 8A and 8B.Particularly, FIG. 8A is a graph showing the voltage that appears whenapplying a current at an operating temperature of 100° C. depending onthe capacity, and FIG. 8B is a graph showing the results of measurementof gas evolution at the same time.

Test Example 5

For the lithium-air battery of Preparation Example 5 and the lithium-airbattery of Preparation Example 7, the voltage and power density weremeasured by applying current of 0.01 mA/s at a temperature of 100° C.The results thereof are shown in FIGS. 9A and 9B. With reference toFIGS. 9A and 9B, the power density was increased 10 times or more whenusing the cathode of Preparation Example 3 (the results of measurementof the lithium-air battery of Preparation Example 5 are shown in FIG. 9Aand the results of measurement of the lithium-air battery of PreparationExample 7 are shown in FIG. 9B).

Test Example 6

For the lithium-air batteries of Preparation Example 6 and PreparationExample 7, the surface of the cathode was observed before and afterdischarge using a scanning electron microscope (SEM). The resultsthereof are shown in FIGS. 10A to 10C. FIG. 10A shows the surface of thecathode before discharge of the lithium-air battery of PreparationExample 6, and FIG. 10B shows the surface of the cathode after dischargeof the lithium-air battery of Preparation Example 6 at a temperature of150° C. FIG. 10C shows the surface of the cathode after discharge of thelithium-air battery of Preparation Example 7 at a temperature of 100° C.As shown in the SEM images, it was confirmed that the operatingtemperature was different but the same discharge product was generatedafter discharge.

Although the exemplary embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A method of manufacturing an electrolyte membranefor a lithium-air battery, comprising: preparing an inorganic salt;preparing an inorganic melt admixture comprising the inorganic salt;immersing a separator in the inorganic melt admixture; and drying theimmersed separator.
 2. The method of claim 1, wherein the inorganic saltcomprises at least two nitrogen-oxide compounds.
 3. The method of claim1, wherein the inorganic salt comprises one or more selected from thegroup consisting of lithium nitrate (LiNO₃), potassium nitrate (KNO₃),potassium nitrite (KNO₂), cesium nitrate (CsNO₃), sodium nitrate(NaNO₃), and calcium nitrate (Ca(NO₃)₂).
 4. The method of claim 1,wherein the inorganic salt comprises two types of nitrogen-oxidecompounds, three types of nitrogen-oxide compounds, four types ofnitrogen-oxide compounds, or five types of nitrogen-oxide compounds. 5.The method of claim 4, wherein the two types of the nitrogen-oxidecompounds comprise lithium nitrate and potassium nitrate, the threetypes of the nitrogen-oxide compounds comprise lithium nitrate,potassium nitrate and sodium nitrate; comprise lithium nitrate,potassium nitrate and calcium nitrate; or comprise lithium nitrate,potassium nitrite and cesium nitrate, the four types of thenitrogen-oxide compounds comprise lithium nitrate, potassium nitrate,sodium nitrate and calcium nitrate, and the five types of thenitrogen-oxide compounds comprise lithium nitrate, potassium nitrate,cesium nitrate, sodium nitrate and calcium nitrate.
 6. The method ofclaim 1, wherein the inorganic salt comprises: the three types of thenitrogen-oxide compounds comprising lithium nitrate, potassium nitriteand cesium nitrate, the four types of the nitrogen-oxide compoundscomprising lithium nitrate, potassium nitrate, sodium nitrate andcalcium nitrate, or the five types of the nitrogen-oxide compoundscomprising lithium nitrate, potassium nitrate, cesium nitrate, sodiumnitrate and calcium nitrate.
 7. The method of claim 6, wherein the threetypes of the nitrogen-oxide compounds comprise an amount of about 29 mol% to 35 mol % of lithium nitrate, an amount of about 51 mol % to 56 mol% of potassium nitrite and an amount of about 10 mol % to 15 mol % ofcesium nitrate, the four types of the nitrogen-oxide compounds comprisean amount of about 27 mol % to 31 mol % of lithium nitrate, an amount ofabout 38 mol % to 50 mol % of potassium nitrate, an amount of about 11mol % to 20 mol % of sodium nitrate and an amount of about 10 mol % to13 mol % of calcium nitrate, and the five types of the nitrogen-oxidecompounds comprise an amount of about 14 mol % to 17 mol % of lithiumnitrate, an amount of about 29 mol % to 31 mol % of potassium nitrate,an amount of about 28 mol % to 32 mol % of cesium nitrate, an amount ofabout 9 mol % to 11 mol % of sodium nitrate and an amount of about 13mol % to 18 mol % of calcium nitrate, all the mol % based on the totalmole of the nitrogen-oxide compounds.
 8. The method of claim 1, whereinthe inorganic salt has a eutectic point of about 130° C. or less.
 9. Themethod of claim 6, wherein the inorganic salt has a eutectic point ofabout 100° C. or less.
 10. An electrolyte membrane for a lithium-airbattery manufactured by a method of claim
 1. 11. A method ofmanufacturing a cathode for a lithium-air battery, comprising: preparinga metal precursor admixture comprising a metal precursor; preparing anelectrode slurry comprising the metal precursor admixture and a carbonmaterial; applying the electrode slurry on a substrate; and reducing ametal ion by applying current to the applied electrode slurry.
 12. Themethod of claim 11, wherein the metal precursor comprises one or moreselected from the group consisting of platinum (Pt), rubidium (Ru),palladium (Pd), rhodium (Rh), nickel (Ni), cobalt (Co), iron (Fe),copper (Cu), and silver (Ag).
 13. The method of claim 11, wherein thecarbon material comprises one or more selected from the group consistingof natural graphite, artificial graphite, carbon nanotubes, reducedgraphene oxide (rGO), carbon fiber, carbon black, Ketjen black,acetylene black, mesoporous carbon, graphite, Denka black, fullerene,and activated carbon.
 14. The method of claim 11, wherein the electrodeslurry comprises the metal precursor in an amount of about 40 parts byweight to 60 parts by weight based on 100 parts by weight of the carbonmaterial.
 15. The method of claim 11, wherein the current is applied forabout 0.1 sec to 60 sec.
 16. The method of claim 11, wherein a magnitudeof the current is about 6 A to 10 A.
 17. A cathode for a lithium-airbattery manufactured by a method of claim
 11. 18. A lithium-air battery,comprising: a cathode comprising a carbon material; an anode disposed toface the cathode and comprising a lithium metal that receives andreleases a lithium ion; and an electrolyte membrane of claim 10,interposed between the cathode and the anode.
 19. The lithium-airbattery of claim 18, wherein the carbon material comprises one or moreselected from the group consisting of natural graphite, artificialgraphite, carbon nanotubes, reduced graphene oxide (rGO), carbon fiber,carbon black, Ketjen black, acetylene black, mesoporous carbon,graphite, Denka black, fullerene, and activated carbon.